This book constitutes the refereed proceedings of the 12th International Conference on Tests and Proofs, TAP 2018, held as part of STAF 2018, in Toulouse, France, in June 2018.The 8 regular papers, 2 short papers, 1 invited paper and 1 invited tutorial presented in this volume were carefully reviewed and selected from 18 submissions. The TAP conference promotes research in verification and formal methods that targets the interplay of proofs and testing: the advancement of techniques of each kind and their combination, with the ultimate goal of improving software and system dependability.